The roles of cyclic nucleotides and protein kinases in normal vision and in retinal degeneration have been further examined: l. A new calcium phospholipid-dependent protein kinase (C-kinase) has been identified in retinal photo-receptors. 2. Protein tyrosine kinase has also been partially characterized in human retinoblastoma cells. 3. From genetic crosses of rd and rds mouse mutants we have found that the genes affect retinal cyclic nucleotide metabolism in different manners but each ultimately leads to photoreceptor cell death. 4. In a case of human choroideremia, aberrently high levels of cyclic AMP were found in the pigment epithelium-choroid unit and thus may be involved in the etiology of the disease.